Coordinate measuring machines serve to measure workpieces, for example in order to check the dimensional accuracy of workpieces during production. To this end, a probe pin is fastened to a movable arm of the coordinate measuring machine and is therefore guided in contact with the workpiece. The position which the arm has when the probe pin touches the workpiece is ascertained and a surface point on the workpiece is determined therefrom. Conclusions can then be drawn about the surface contour of the workpiece to be measured from a multiplicity of measurements of points sensed in this way. Further measuring methods, in which the surface is measured by way of a coordinate measuring machine, not in a manner which makes contact at points, but rather, for example, in a manner which tracks line by line, are to be mentioned for the sake of completeness. It will be obvious that the arrangement which is described in the following text can be used for all known coordinate measuring machines.
A problem in the case of conventional coordinate measuring machines then consists in that complexly shaped workpieces also have to be sensed, for example engine blocks including the holes which are provided therein. This requires the probe pin to optionally be arranged in an inclined manner with respect to the arm, for instance in order to be introduced into an oblique hole. Here, the required inclination, the spacing of a probe pin tip from the arm, etc. are different from workpiece to workpiece. Spacer and aligning elements have therefore been placed up to now between the work pin carrier on the arm and the probe pin tip which is typically composed of very hard material and can be formed, for example, as a ruby ball. Accordingly, the tip of the probe pin is typically arranged on a suitable, thin rod which can be formed, for example, from carbon fiber reinforced plastic or hard metal, said rod in turn being anchored in a screw-in thread, by way of which the entire probe pin which is formed in this way can be fastened to one intermediate element, designed as spacer or aligning element, or to the arm.
It is then a problem if the probe pin with the small tube axis neither stands perpendicularly on the coordinate measuring machine-side support face of the arm, from which support face the arm rises up slightly upon contact, nor is exactly perpendicular with respect to said bearing face. In a case of this type, it is namely necessary to arrange the probe pin itself in an inclined or pivoted manner with respect to the probe pin carrier of the coordinate measuring machine. Here, inclinations about at least one axis have to be fixed in two directions; this requires the spacer elements to be of suitable configuration.
Probe pins are then subject to wear. Said wear can be a result both of reaming or abrasion on the probe pin ball during scanning measurement and of mechanical destruction, etc. As a result, a change of the probe pins becomes necessary. After a change of this type, the probe pin ball of a new probe pin has to be arranged exactly in the same, reproduced position as previously in the case of the old probe pin, in order to avoid measuring errors. If this is not ensured, the measured values are also no longer reproducible after a change of the probe pin, which possibly results in considerable calibration work. It will be obvious that the probe pin also has to be aligned as previously.
Clamping elements have previously been used to achieve an inclined arrangement, by way of which the pivoted or inclined position of a probe pin receptacle was fixed frictionally. The corresponding arrangements were difficult to set, that is to say imprecise, which is very disruptive, in particular, in the case of a change between different workpieces to be measured and, moreover, entails low reproducibility despite high costs of the element.
It is desirable to provide an option, by way of which probe tips can be arranged obliquely with respect to probe pin carriers of a coordinate measuring machine in a simple, inexpensive and reproducible way.
It is the object of this invention to provide something novel for industrial use.
The solution of this problem is claimed in independent form. Preferred embodiments are found in the subclaims.